The AN524 has more interrupt lines than the AN505 and AN521; make
numirq board-specific rather than a compile-time constant.

Since the difference is small (92 on the current boards and 95 on the
new one) we don't dynamically allocate the cpu_irq_splitter[] array
but leave it as a fixed length array whose size is the maximum needed
for any of the boards.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210215115138.20465-10-peter.maydell@linaro.org